TPS54341_15 datasheet(30/48 Pages) TI

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OUT

0.25

3.5 A

0.25

331 mV

4.4

600 kHz

(

)

(

)

(

)

(

)

(

)

(

)

OUT

IN min

OUT

CI rms

IN min

6 V - 3.3 V

3.3 V

3.5 A

1.74 A

6 V

TPS54341

SLVSC61 – NOVEMBER 2013

www.ti.com

Input Capacitor

The TPS54341 device requires a high-quality ceramic-type X5R or X7R input-decoupling capacitor with at least 3

μF of effective capacitance. Some applications will benefit from additional bulk capacitance. The effective

capacitance includes any loss of capacitance due to dc bias effects. The voltage rating of the input capacitor

must be greater than the maximum input voltage. The capacitor must also have a ripple current rating greater

than the maximum input current ripple of the TPS54341 device. The input ripple current can be calculated using

Equation 41.

The value of a ceramic capacitor varies significantly with temperature and the dc bias applied to the capacitor.

The capacitance variations due to temperature can be minimized by selecting a dielectric material that is more

stable over temperature. X5R and X7R ceramic dielectrics are usually selected for switching regulator capacitors

because they have a high capacitance to volume ratio and are fairly stable over temperature. The input capacitor

must also be selected with consideration for the dc bias. The effective value of a capacitor decreases as the dc

bias across a capacitor increases.

For this example design, a ceramic capacitor with at least a 42 V voltage rating is required to support the

maximum input voltage. Common standard ceramic capacitor voltage ratings include 4 V, 6.3 V, 10 V, 16 V, 25

V, 50 V, or 100 V. For this example, two 2.2-

μF 100-V capacitors in parallel are used. Table 1 shows several

choices of high voltage capacitors.

The input capacitance value determines the input ripple voltage of the regulator. The input voltage ripple can be

calculated using Equation 42. Using the design example values, IOUT = 3.5 A, CIN = 4.4 μF, ƒSW = 600 kHz, yields

an input voltage ripple of 331 mV and a rms input ripple current of 1.74 A.

(41)

(42)

Table 1. Capacitor Types

VENDOR

VALUE (

μF)

EIA Size

VOLTAGE (V)

DIALECTRIC

COMMENTS

1 to 2.2

100

1210

GRM32 series

1 to 4.7

Murata

100

1206

GRM31 series

1 to 2.2

1 to 1.8

2220

1 to 1.2

100

Vishay

VJ X7R series

1 to 3.9

2225

1 to 1.8

100

X7R

1 to 2.2

100

1812

C series C4532

1.5 to 6.8

TDK

1 to 2.2

100

1210

C series C3225

1 to 3.3

1 to 4.7

1210

100

AVX

X7R dielectric series

1 to 4.7

1812

1 to 2.2

100

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